The invention is generally related to apparatus for comminuting ore, and is specifically directed to an improved liner assembly for an ore grinding mill used in commercial mining operations and an insert used in conjunction with the liner assembly to facilitate removal of worn liner segments. The invention represents an improvement of the invention disclosed in commonly owned U.S. Pat. No. 4,165,041, which issued Aug. 21, 1979.
Ore grinding mills typically consist of a large cylindrical drum which is rotated about a horizontal axis. The axial ends of the drum are open, and the material to be comminuted is continuously fed into the mill at one end with the comminuted product continuously emerging from the other end.
Many ores such as taconite (iron ore) are extremely hard and highly abrasive. In order to maintain continuous operation of the grinding mill, it is necessary to provide a wear liner for the drum which is highly abrasion-resistant, and which also is tough enough to withstand the continuous impact of ore fragments. Grinding mills of this type may also employ rods or balls to assist in the comminuting process, which further compounds the problem of wear.
Abrasion-resistant liners are necessarily segmented (i.e., constructed from a plurality of components) for a number of reasons, including the limited size of narrow access openings and the significant size and weight of the liner taken as a whole. Current ore comminuting mills reach diameters of 40 feet. The wear liner is therefore typically constructed from a plurality of wear segments which may be aligned both axially and circumferentially on the inner surface of the mill shell and/or ends.
The individual liner segments of conventional liner assemblies are mounted in spaced relation so that gaps exist between each segment and the adjacent segment or segments. This is done for several reasons, one of which is that there must be a degree of tolerance to accommodate the various segments. It would be possible to construct a liner assembly from a plurality of segments the dimensions of which are machined to close tolerances, but this is not economically feasible for the relatively large wear segments which are typically formed from pearlitic or martensitic steel, or white iron.
The problem created by having gaps between adjacent segments is that the particulate material resulting from the comminution process becomes lodged in the gaps and causes the wear segments to stick together. This problem is more acute with mills having ball media because balls tend to fragment with increased wear, and these particles also enter and become lodged in the gaps. Peening of the segments likewise increases with usage, also forcing the individual segments together. The combined effect of particulate material forced between the gaps and segment peening results in the liner assembly becoming integral (i.e., the segments become interconnected), which increases the difficulty of removing the individual liner segments when replacement is necessary. Often, removal of the segments takes considerably more time than installation, resulting in substantial down time of the mill. This has serious economic effects, since many ore processing plants operate 24 hours a day.
The invention of U.S. Pat. No. 4,165,041 offered a solution to this problem by configuring each liner segment to have tapered longitudinal sides and ends, with the taper creating an undercut with the liner segment mounted on the cylindrical shell. As configured, the adjacent wear segments disclosed in the patent define a pocket therebetween which is generally triangular in cross-section and extends either the length and/or the width of the wear segments.
The invention of U.S. Pat. No. 4,165,041 further comprised a wedge or triangularly shaped insert placed into each pocket, where it is loosely retained. The length of the insert corresponds in length to the segment length or width, depending on the application. The use of inserts in the triangular pockets in effect prevents particulate matter from entering the pockets, thus preventing the buildup of material which makes segment removal difficult.
This invention represents an improvement to the insert of U.S. Pat. No. 4,165,041, and specifically addresses a problem sometimes encountered when the sides and/or ends of the liner segment leave an undersized pocket relative to the size of the insert. As indicated above, it is not economically feasible for steel or iron to be cast in close tolerance for wear segments of this type, and if the gaps between adjacent liner segments are undersized (i.e., the liner segments are oversized), the inserts may have the effect of preventing the liner segments from seating properly, or it is difficult if not impossible to place the inserts in the liner assembly.
It has been found that this problem can be overcome by forming a recess or groove in the bottom surface of the insert which, in the preferred embodiment, is a V-groove that corresponds to the configuration of the insert itself. In essence, this results in an insert having two diverging legs which can collapse together to the degree required if the pocket between liner segments is undersized.
The preferred embodiment of the improved insert is also formed with a leg that projects upwardly from the generally triangular body having a length that is sufficient to project above at least a portion of the adjacent liner segments. This facilitates proper placement of the insert at the time the liner assembly is installed.
The invention will be more fully appreciated from the drawings and specification.